ULTRASONIC MACHINING PROCESS (USM)
PRINCIPLE OF ULTRASONIC MACHINING PROCESS (USM):
Ultrasonic machining (USM) is the elimination of material by the abrading action of micro stones-loaded liquid slurry available between the work piece and a tool which is vibrating at a 90 degree angle to the work surface at a frequency more than the audible range. USM, also known as ultrasonic collision grinding, is a machining operation in which abrasive slurry particles are generously flows between the work piece and a vibrating tool. This process varies from most other machining methods since in this process a very little amount of heat is generated on the work piece. The tool material will not contacts the work material and as a result the grinding force is infrequently more, which makes this operation perfect for machining tremendously hard and brittle materials, such as glass, ruby, graphite, diamond, sapphire and ceramics.
The working course of action of an ultrasonic machining is done when the tool interacts with the work piece or the medium to be treated. The tool is subjected to vibration in a particular direction, frequency and intensity. The vibrations are produced by a transducer and are transmitted to the tool using a vibration transmission system, often with an alteration in direction and amplitude. The structure of the ultrasonic machine is dependent on the process being performed by its tool.
Ultrasonic Machining Machine
CHARACTERISTICS OF ULTRASONIC MACHINING PROCESS (USM):
i. The USM process is done by selecting a desirable tool along-with abrasives slurry as a working media.
ii. Generally the cutting tool oscillates at the frequency range of 20 KHZ to 40 KHZ.
iii. Always the shape of tool is similar to the shape requirements in the work piece.
iv. The abrasive grains are actuated by the high speed reciprocate motions across the small gap, in between the tool and the work piece.
v. Uniform force is applied to progressively feed the tool.
vi. The impact of abrasive particles is the energy source which is mainly responsible in removal of the material, through the form of small wear particles which are carried away by the abrasive slurry.
Ultrasonic Machining consists of:
1. High Power sine wave generator
2. Magneto- striction Transducer
3. Tool Holder
Ultrasonic Machining Process
The magnetostrictor used in USM, is shown in above figure has a high-frequency winding wound on a magnetostrictor core and a special polarizing winding around an armature. The magnetostriction effect was first exposed by Joule at Manchester in the year of 1874. Magnetic field undergoing ultrasonic frequencies causes corresponding changes in a ferromagnetic object placed within its region of influence.
This outcome is used to oscillate the USM tool, which is mounted at the last part of a magnetostrictor, at ultrasonic frequencies (18 to 20 kHz). The method of action of a magnetostrictor can be explained as follows.
Coefficient of magnetostriction elongation is calculated by using the following formula (em) = ( ∆l/l )
Here, Δl – Incremental length of the magnetostrictor (mm)
l- Length of the magnetostrictor core (mm)
Process parameters of USM:
1. Amplitude of vibration (15 to 50 microns)
2. Frequency of vibration (19 to 25 kHz).
3. Feed force (F) related to tool dimensions.
4. Feed pressure.
5. Abrasive size.
6. Abrasive materials: (Al203, SiC, B4C, Boron silicarbide, Diamond)
7. Flow strength of the work material.
8. Flow strength of the tool material.
9. Contact area of the tool.
10. Volume concentration of abrasive in water slurry.
11. Tool characteristics:
a. Material of tool
c. Amplitude of vibration
d. Frequency of vibration
e. Strength developed in tool
12. Work material characteristics:
b. Impact strength
c. Surface fatigue strength
13. Slurry material characteristics:
a. Abrasive – hardness, size, shape and quantity of abrasive flow
b. Liquid – Chemical property, viscosity, and flow rate.
ADVANTAGES OF ULTRASONIC MACHINING PROCESS:
i. There is no direct contact of the tool and workpiece. since the slurry used, it makes it a wet cutting process.
ii. The surfaces produced are free from stress and damages.
iii. Free from burrs and distortions.
iv. suitable for machining brittle materials
v. Good surface finish and structural integrity.
APPLICATIONS OF ULTRASONIC MACHINING PROCESS:
i. This process is capable on hard and brittle alloys, semiconductors, glass, fiber material,
Ceramics, carbides etc.
ii. Machining on auto-engine components.
iii. In machining, wire drawing, punching and blanking of small dies are possible one.
iv. Machining ceramic components for drilling holes in borosilicate glass for the sensors used in electronic industries.
v. Drilling very fine holes in helicopter power transmission shafts and gears.
DISADVANTAGES AND LIMITATIONS OF ULTRASONIC MACHINING PROCESS:
i. Very poor material removal rate.
ii. Relatively high tool wear.
iii. Minimum depth of hole is achieved .